Biogenic fuel gas generation in geologic hydrocarbon deposits

ABSTRACT

A method of increasing biogenic production of a combustible gas from a subterranean geologic formation is described. The method may include extracting formation water from the geologic formation, where the extracted formation water includes at least a first species and a second species of microorganism. The method may also include analyzing the extracted formation water to identify the first species of microorganism that promotes the biogenic production of the combustible gas. An amendment may be introduced to the formation water to promote the growth of the first species of microorganism, and the biological characteristics of the formation water may be altered to decrease a population of the second species in the geologic formation.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of prior application Ser. No. 12/840,909, filed Jul. 21, 2010, which is a continuation of prior application Ser. No. 12/129,441, filed May 29, 2009, which was a continuation of prior application Ser. No. 11/343,429, filed Jan. 30, 2006, which was a continuation-in-part of International Application PCT/US2005/015259, with an international filing date of May 3, 2005. The entire contents of all the above-described applications are hereby incorporated by this reference for all purposes.

FIELD OF THE INVENTION

The present invention relates to methods of rearranging the constituent population of a native consortium of microorganisms to stimulate the growth of consortium members that produce metabolic products such as hydrogen and methane. Rearranging the constituents of the consortium may include diluting the consortium microorganisms with formation water extracted and transported from the geologic formation. It may also include introducing amendments to the native consortium that causes a change in the distribution of metabolic pathways and/or population distributions of consortium members.

BACKGROUND OF THE INVENTION

The formation water present in subterranean geologic formations of oil, coal, and other carbonaceous materials is normally considered an obstacle to the recovery of materials from those formations. In coal mining, for example, formation water often has to be pumped out of the formation and into remote ponds to make the coal accessible to mining equipment. Similarly, formation water has to be separated from the crude oil extracted from a subterranean field and disposed of typically underground. The extraction, separation and disposal of the formation water add costs to recovery processes, and generate a by-product regarded as having little value.

Further investigation, however, has revealed that even extracted formation water can support active communities of microorganisms from the formation. The presence of these microorganism in the formation environment were known from previous recovery applications, such as microbially enhanced oil recovery (MEOR), where the microorganisms naturally generate surface active agents, such as glycolipids, that help release oil trapped in porous substrates. In MEOR applications, however, it was generally believed that the microorganisms were concentrated in a boundary layer between the oil and water phases. The bulk formation water was believed to be relatively unpopulated, because it lacked a hydrocarbon food source for the microorganisms. More recent studies have shown that robust populations of microorganisms do exist in the bulk formation water, and can even survive extraction from the geologic formation under proper conditions.

The discovery of active populations of microorganisms in bulk formation water has come at a time when new applications are being envisioned for these microorganisms. For years, energy producers have seen evidence that materials like methane are being produced biogenically in formations, presumably by microorganisms metabolizing carbonaceous substrates. Until recently, these observations have been little more than an academic curiosity, as commercial production efforts have focused mainly on the recovery of coal, oil, and other fossil fuels. However, as supplies of easily recoverable natural gas and oil continue to dwindle, and interest grows using more environmentally friendly fuels like hydrogen and methane, biogenic production methods for producing these fuels are starting to receive increased attention.

Unfortunately, the techniques and infrastructure that have been developed over the past century for energy production (e.g., oil and gas drilling, coal mining, etc.) may not be easily adaptable to commercial-scale, biogenic fuel production. Conventional methods and systems for extracting formation water from a subterranean formation have focused on getting the water out quickly, and at the lowest cost. Little consideration has been given to extracting the water in ways that preserve the microorganisms living in the water. Similarly, there has been little development of methods and systems to harness microbially active formation water for enhancing biogenic production of hydrogen, methane, and other metabolic products of the microbial digestion of carbonaceous substrates. Thus, there is a need for new methods and systems of extracting, treating, and transporting formation water within, between, and/or back into geologic formations, such that microbial activity in the water can be preserved and even enhanced.

New techniques are also needed for stimulating microorganisms to produce more biogenic gases. Native consortia of hydrocarbon consuming microorganisms usually include many different species that can employ many different metabolic pathways. If the environment of a consortium is changed in the right way, it may be possible to change the relative populations of the consortium members to favor more combustible gas production. It may also be possible to influence the preferred metabolic pathways of the consortium members to favor combustible gases as the metabolic end products. Thus, there is also a need for processes that can change a formation environment to stimulate a consortium of microorganisms to produce more combustible biogenic gases.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention relate to methods to stimulate biogenic production of a metabolite with enhanced hydrogen content. The methods may include the steps of forming an opening in a geologic formation to provide access to a consortium of microorganisms, and injecting water into the opening to disperse at least a portion of the consortium over a larger region of a hydrocarbon deposit. The method may also include measuring a change in the rate of production of the metabolite in the formation.

Embodiments of the invention may still further relate to pumping and extraction methods to stimulate the biogenic production of a metabolite with enhanced hydrogen content. The methods may include forming an opening in a geologic formation to provide access to a native consortium of microorganisms. The method may also include injecting a first portion of water into the opening to disperse at least a portion of the consortium over a larger region of a hydrocarbon deposit, extracting formation fluids from the geologic formation following the water injection, and injecting a second portion of the water into the opening after extraction. The methods may also include measuring a change in the rate of production of the combustible gas in the formation.

Embodiments of the invention may also further include methods to stimulate biogenic production of a metabolite with enhanced hydrogen content by changing the salinity level of water in a geologic formation. The methods may include measuring a salinity level of formation water in a geologic formation. The methods may also include forming an opening in the formation to provide access to a consortium of microorganisms, and injecting water into the opening to reduce the salinity level of the formation water in the formation. The methods may additionally include measuring a change in the rate of production of the metabolite in the formation.

Embodiments of the invention still further relate to processes for enhancing a consortium of microorganisms to make materials with enhanced hydrogen content from carbonaceous substrates in an anaerobic environment. The processes may include extracting formation water from a geologic formation, and removing at least a portion of an extractable material from the formation water to make amended formation water. This extractable material may include microorganisms that are filtered out of water. The processes may further include introducing the amended formation water to the carbonaceous material.

Embodiments of the invention may also relate to processes for increasing biogenic hydrocarbon production in a geologic formation containing a carbonaceous material. The processes may include extracting formation water from the formation, and removing at least a portion of one or more hydrocarbons from the formation water to make amended formation water. Microorganisms in water may also be filtered and/or sterilized to make the amended formation water. The processes may further include reintroducing the amended formation water to the geologic formation.

Embodiments of the invention may also further relate to processes for transporting formation water between geologic formations. The processes may include extracting the formation water from a first formation, and removing at least a portion of a hydrocarbon from the formation water to make amended formation water. Microorganisms in water may also be filtered and/or sterilized to make the amended formation water. The processes may also include transporting the amended formation water to a second geologic formation, and introducing the amended formation water to the carbonaceous material in the second geologic formation. Microorganisms may also be extracted from the first formation and introduced to the second formation with the amended formation water.

Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the invention. The features and advantages of the invention may be realized and attained by means of the instrumentalities, combinations, and methods described in the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method of intraformation transport of formation water according to embodiments of the invention;

FIG. 2 is a flowchart illustrating a method of transporting of formation water between formations (i.e., interformation transport) according to embodiments of the invention;

FIG. 3 shows a system for the transporting of formation water within a formation (i.e., intraformation transport) according to embodiments of the invention;

FIG. 4 shows a system for interformation transport of formation water according to embodiments of the invention;

FIGS. 5A-B are flowcharts illustrating methods according to embodiments of the invention of using water to stimulate biogenic gas production by a consortium of microorganisms;

FIGS. 6A-B are flowcharts illustrating methods according to embodiments of the invention of controlling the salinity level of the water in a geologic formation; and

FIG. 7 is a plot of the percentage of methane in the headspace of a sealed coal container over time for three levels of added formation water.

DETAILED DESCRIPTION OF THE INVENTION

Methods of stimulating the production of biogenic metabolites with enhanced hydrogen content (e.g., combustible gases such as methane and hydrogen) by changing the makeup of a consortium of microorganisms are described. The changes may be brought about by diluting a native consortium in water to disperse consortium members over a larger region of a geologic formation. The dispersion can create opportunities for the microorganism to grow with less competition from consortium members that do not generate metabolites with enhanced hydrogen content. When the microorganisms are spread out over a larger region of a carbonaceous substrate (e.g., a hydrocarbon deposit such as an oil or coal bed) the microorganism that are most effective at utilizing the substrate as a food source are expected to grow at the fastest rates. In an anaerobic formation environment, those metabolic processes typically include the conversion of the substrate to biogenic gases such as hydrogen and methane, among other gases, as well as acetate (e.g., acetic acid). Consequently, the dispersion of the consortium in water is expected to increase population growth for those microorganism species that are more efficient at converting hydrocarbon substrates into metabolic products having enhanced hydrogen content such as hydrogen and methane.

While the aqueous dispersion may favor the growth of the hydrocarbon metabolizers over other consortium members, it may not have as great an impact on the favored metabolic pathways of the metabolizers. For example, a methanogenic microorganism may be able to convert the hydrocarbon substrate into either methane or acetate. Embodiments of the invention also include methods of stressing the microorganism to favor metabolic pathways that produce a target metabolic product (e.g., hydrogen, methane, etc.) over other products (e.g., acetate, ammonia, hydrogen sulfide, carbon dioxide etc.). These methods include introducing an amendment to the formation environment surrounding the microorganism consortium that may have an effect on the metabolic pathways at least some of the consortium members favor. The amendment may include a metabolite (i.e., a chemical intermediary or product of a metabolic process) generated by some of the consortium members. By concentrating the consortium environment with the metabolite, the consortium members may be influenced to favor a different metabolic pathway that does not produce even more of the metabolite. Alternatively, a rate limiting metabolite may be introduced that normally causes a bottleneck in a metabolic pathway. Introducing this amendment to the consortium environment may stimulate more use of the pathway to consume the added metabolite.

The water used for the dilution and dispersion of the consortium may come from a variety of sources. One source that may be in close proximity to the formation is formation water. Systems and methods for the transport of anaerobic formation water from a subterranean geologic formation are described. “Anaerobic” formation water is characterized as having little or no dissolved oxygen, in general no more than 4 mg/L, preferably less than 2 mg/L, most preferably less than 0.1 mg/L, as measured at 20 degrees C. and 760 mmHg barometric pressure. During application of the present invention, higher levels of dissolved oxygen, greater than 4 mg/L, can be tolerated without appreciably degrading microorganism performance, for limited times or in certain locations such as a surface layer in a storage or settling tank. Dissolved oxygen can be measured by well-known methods, such as by commercially-available oxygen electrodes, or by the well-known Winkler reaction.

The formation water may be extracted and then reintroduced into the same formation in an intraformation transport process, or introduced into a different formation in an intraformation transport process. The formation water may be analyzed to determine the chemical composition of the water, and to ascertain whether microorganisms are present. When microorganisms are present, they may also be identified by genus and/or species.

The choice of formation water may be influenced by the content and/or activity of the microorganism found in the water. For example, a first formation having native formation water containing high concentrations of a microorganism of interest may be transported to a second formation to attempt to stimulate the growth of the microorganism in the second formation. The water transported to the new formation may contain a population of the microorganism, which may act as a seed population for the growth of the microorganism in the second formation.

The formation water may be amended based on the analysis of the compounds and microorganisms present in the native water. These amendments may include changing the composition of the formation water to enhance the growth of one or more species of the microorganisms present. For example, the amendments may include adjusting the microorganism nutrient levels, pH, salinity, oxidation potential (Eh), and/or metal ion concentrations, among other compositional changes to the formation water. The amendments may also include filtering and/or processing the formation water to reduce the concentration of one or more chemical and/or biological species.

Amended or unamended, the extracted formation water is transported back to the same formation, or a different formation. For example, intraformation transport may include cycling the formation water through the formation one or more times, where the water may be extracted from the formation, amended, and returned to the formation in a continuous loop process. Interformation transport may include, for example, extracting formation water from a first formation and transporting it (treated or untreated) to a second subterranean formation that has carbonaceous materials, but little or no native formation water and/or microorganisms. The aqueous environment introduced to the second formation creates conditions for microorganism populations to grow and convert the carbonaceous material into hydrogen, smaller hydrocarbons (e.g., butane, propane, methane), and other useful metabolites.

Referring now to FIG. 1, a flowchart is shown that illustrates a method of intraformation transport of formation water according to embodiments of the invention. The method starts with the accessing the formation water 102 in a geologic formation. The geologic formation may be a previously explored, carbonaceous material containing, subterranean formation, such as a coal mine, oil field, natural gas deposit, carbonaceous shale, etc. In many of these instances, access to the formation water can involve utilizing previously mined or drilled access points to the formation. For unexplored formations, accessing the formation water may involve digging, or drilling through a surface layer to access the underlying water.

Once the formation water is accessed, it may be extracted from the formation 104. The extraction may involve bringing the formation water to the surface using one or more hydrologic pumping techniques. These techniques may include pumping the formation water to the surface using a pumping device that harnesses electrical, mechanical, hydraulic, pneumatic, and/or fluid-expansion type forces, among other modes of action.

The extracted formation water may be analyzed 106 to ascertain information about the chemical and biological composition of the water. Chemical analyses may include spectrophotometry, NMR, HPLC, gas chromatography, mass spectrometry, voltammetry, and other instrumentation and chemical tests. The tests may determine the presence and concentrations of elements like carbon, phosphorous, nitrogen, sulfur, magnesium, manganese, iron, calcium, zinc, tungsten, and titanium, among others. The tests may also detect the presence and concentrations of polyatomic ions, such as PO₄ ²⁻, NH₄ ⁺, NO₂ ⁻, NO₃ ⁻, and SO₄ ⁻, among others. Biological analyses may include techniques and instrumentation for detecting genera and/or species of one or more microorganisms present in the formation water. These test may include genus and/or species identification of anaerobes, aerobes, microaerophiles, etc. found in the formation water. Additional details for identifying and isolation genera and species of microorganisms from the formation water are described in commonly assigned U.S. patent application Ser. No. 11/099,879, filed Apr. 5, 2005, and titled “Systems and Methods for the Isolation and Identification of Microorganisms from Hydrocarbon Deposits”, the entire contents of which are hereby incorporated by reference for all purposes.

The formation water may also be amended 108 by, for example, altering one or more physical (e.g., temperature), chemical, or biological characteristics of the water. As noted above, the amendments may include adjustments to the chemical composition of the formation water, including the increase or decrease of a microorganism nutrient level, pH, salinity, oxidation potential (Eh), and/or metal ion concentration, among other chemical species. For example, changes in microorganism nutrient levels may include changes in formation water concentration of cationic species, such as ammonium, calcium, magnesium, sodium, potassium, iron, manganese, zinc, and copper, among other cationic species. It may also include changes in anionic species, such as nitrate, nitrite, chloride, carbonate, phosphate, acetate, and molybdate, among other anionic species. It may further include changes in the nutrient level of compounds including di-sodium hydrogen phosphate, boric acid, yeast extract, peptone, and chelating compounds like nitrilotriacetic acid, among other compounds.

Changes in the biological characteristics of the formation water may include increasing or decreasing the population of one or more genera and/or species of microorganism in the water. Genera whose population in the formation water may be controlled include, Thermotoga, Pseudomonas, Gelria, Clostridia, Moorella, Thermoacetogenium, Methanobacter, Bacillus, Geobacillus, Methanosarcina, Methanocorpusculum, Methanobrevibacter, Methanothermobacter, Methanolobus, Methanohalophilus, Methanococcoides, Methanosalsus, Methanosphaera, Granulicatella, Acinetobacter, Fervidobacterium, Anaerobaculum, Ralstonia, Sulfurospirullum, Acidovorax, Rikenella, Thermoanaeromonas, Desulfovibrio, Dechloromonas, Acetogenium, Desulfuromonas, Ferribacter, and Thiobacillus, among others. Additional description of microorganisms, and consortia of microorganisms, that may be present and controlled in the formation water can be found in commonly assigned U.S. patent application Ser. No. 11/099,881, filed Apr. 5, 2005, and titled “Generation of materials with Enhanced Hydrogen Content from Anaerobic Microbial Consortia”; and U.S. patent application Ser. No. 11/099,880, also filed Apr. 5, 2005, titled “Generation of Materials with Enhanced Hydrogen Content from Microbial Consortia Including Thermotoga”, the entire contents of both applications hereby being incorporated by reference for all purposes.

Whether amended or not, the extracted formation water may be reintroduced back into the geologic formation 110. The formation water may be reintroduced at or near the location where the water is extracted, or at a position remote from the extraction location. The remote position may or may not be in fluid communication with the extraction location (e.g., a cavity in the formation that is hydraulically sealed from the point where the formation water is extracted).

The formation water may be maintained in an anaerobic state during the extraction, pumping, transport, storage, etc., by using a closed system throughout and displacing the oxygen present in the system with an inert gas, such as argon, substantially pure nitrogen, and/or helium, among other inert gases. The system may also be pressurized with the inert gas to reduce the amount of ambient oxygen that enters the system. Embodiments of anaerobic formation water extraction, transport and storage systems may include low pressure pumps (e.g., vein, fin, and/or rotary pumps, which may use needle, ball and/or butterfly valves) that may be submersible in the subterranean formation water deposit. The conduits and storage elements of the system may be made of oxygen impermeable and chemically inert materials that minimize the diffusion of free oxygen and other contaminants into the anaerobic formation water. Examples of these materials may include butyl rubber, viton, glass, copper, steel, and stainless steel, among other materials.

FIG. 2 shows another flowchart illustrating a method of interformation transport of formation water according to embodiments of the invention. Similar to embodiments of methods of intraformation transport shown in FIG. 1, interformation transport may include accessing the formation water 202 in a first geologic formation, and extracting the water 204 from the first formation. The extracted formation water may be analyzed 206, and amended 208 by altering one or more physical, chemical, and/or biological characteristics of the water.

The formation water may then be transported to a second geologic formation 210. A variety of mechanisms are contemplated for transporting the formation water between the two geologic formations. These include pumping the water through a pipeline that is in fluid communication between the formations. They also include filling containers (e.g., barrels) with formation water and transporting them by vehicle (e.g., car, truck, rail car) to the second formation site. Alternatively, a vehicle designed for the transport of fluids (e.g., a tanker truck, tanker rail car, etc.) may be filled with the formation water at the first formation site and driven (or pulled) to the second formation site.

When the formation water arrives at the second formation site, it is introduced into the second geologic formation 212. The second geologic formation may be a dry formation, where the formation water is pumped into a cavity, network of channels, etc. having little or no detectable levels of native formation water. Alternatively, substantial amounts of native formation water may be present in the second formation, and the water from the first formation is mixed with this native water as it is introduced into the second formation.

FIG. 3 shows a system 300 for intraformation transport of formation water according to embodiments of the invention. The system 300 may include a pump system 302 and amendment system 304 that are positioned on the surface above a subterranean geologic formation 306. The geologic formation 306 may include a formation water stratum 308 that sits below a liquid hydrocarbon layer 310 (e.g., a crude oil containing stratum), which, in turn, may sit below a gas layer 312 (e.g., a natural gas layer). A conduit 314 may be inserted into the formation and positioned such that a distal end of the conduit 314 receives formation water from the stratum 308 and transports it to pump 302 on the surface. In some examples, the conduit 314 may be part of a previous system used to recover hydrocarbons for the formation.

The pump system 302 used to bring the formation water to the surface may include one or more pumping devices such as dynamic pumping devices, reciprocating displacement pumping devices, and rotary displacement pumping devices, among others.

Dynamic pumping devices may include centrifugal pumps, such as axial flow centrifugal pumps, mixed flow and/or radial flow pumps, peripheral pumps, and combinations of these pumps. Axial flow pumps may include single-stage or multi-stage, closed impeller, open impeller (e.g., fixed-pitch or variable-pitch) and combinations of these pumps. Mixed flow and/or radial flow centrifugal pumps may include single suction or double suction, self-priming, non-priming, single-stage, or multi-stage, open-impeller, semiopen-impeller, closed-impeller, and combinations of these types of pumps. Peripheral centrifugal pumps may include single-stage or multi-stage, self-priming or non-priming, and combinations of these types of pumps. Dynamic pumps may also include jet pumps, gas lift pumps, hydraulic ram pumps, and electromagnetic pumps, among other types of dynamic pumps.

Reciprocating displacement pumping devices may include piston or plunger pumps, including steam pumps (e.g., simplex, duplex, triplex or multiplex steam pumps). These pumps may also include power pumps (e.g., single-acting or double-acting; simplex, duplex, triplex, multiplex, and combinations of these power pumps). Also included are pumps utilizing check valves, whether fixed, mobile, or a combination of these characteristics, and may further include hinged barriers, mobile balls or mobile pistons of appropriate shape, with associated containment devices. Also included in reciprocating displacement pumping devices are diaphragm pumps, including simplex, duplex and multiplex, fluid-operated, mechanically-operated, and combinations of these type of pumps.

Rotary displacement pumping devices include pumps equipped with a single rotor, including vane, piston, flexible member, screw and peristaltic pumps. These pumps may also include pumps equipped with multiple rotors, including gear, lobe, circumferential piston, and screw pumps.

At least part of the pump system 302 may be submerged in a pool of formation water in a subterranean formation. In operation, the submerged pump may agitate the formation water, causing dissolved methane and other gases to be released and rise to the top of the formation. Thus, in some embodiments the pump system 302 may include a gas collection system (not shown) at the well head to transport the released gases out of the formation.

When formation water exits the pump system 302 it may be transported to an amendment system 304 where the water may be analyzed and/or amended before being reintroduced back into the formation 306. The analysis components of the system 304 may include chemical and biological measurement instrumentation (not shown) used to provide data on the chemical and biological composition of the formation water. The system 304 may also include components and equipment to change the physical, chemical and biological composition of the formation water. For example, the system 304 may include components to increase or decrease the temperature of the water. The system may also include components and equipment to filter the formation water to remove selected chemical and/or biological species. Descriptions of systems and method for filtering formation water can be found in co-assigned PCT Patent Application No. PCT/US2005/015188, filed May 3, 2005, and titled “Methanogenesis Stimulated by Isolated Anaerobic Consortia”, the entire contents of which is hereby incorporated reference for all purposes. The amendment system 304 may also include components for increasing or decreasing a microorganism nutrient level, pH, salinity, oxidation potential (Eh), and/or metal ion concentration, among other chemical changes to the water.

Formation water passing through the pump system 302 and the amendment system 304 may then be transported thorough the pipeline 315 back into the formation 306. In the embodiment shown, the formation water is reintroduced into the same formation water layer 308, but at a different point from where the water was originally extracted. Alternatively, the formation water may be introduced back into the formation at another layer, such as where an end of the conduit 316 opens to the gas layer 312.

Referring now to FIG. 4, a system 400 for interformation transport of formation water according to embodiments of the invention is shown. The System 400 include a pump system 402 and an amendment system 404 positioned above a first geologic formation 406. Formation water may be extracted by pump system 402 from a formation water layer 408 through the conduit 414, and analyzed and amended in amendment system 404. The amended formation water may then be loaded into the vehicle 418 which can travel between the first formation 406 and the second geologic formation 420.

When the vehicle 418 is filled with formation water it can travel to pumping system 422 positioned above the second formation 420. An outlet (not shown) on the vehicle 418 may be connected to the pump unit 422 and the formation water may be delivered to a subterranean cavity 424 above a hydrocarbon bed 426, in the second formation 420, via conduit 428. In alternative embodiments (not shown) the vehicle 418 may include pumping equipment on-board to pump the formation water into the cavity 424, without the use of an on-site pumping system 422. In more alternative embodiments, the vehicle 418 may be replaced by a transport pipeline (not shown) that transports the formation water directly between the first and second formations 408 and 420.

The extracted formation water may be used to disperse the constituents of a native consortium over a larger region of carbonaceous material. The aqueous dispersion provides an opportunity for the upstream metabolizers (e.g., the “first-bite” microorganisms that metabolize the hydrocarbon substrate into smaller molecules) and methanogenic microorganisms in the consortium to grow with less interference from nearby competing species that are flushed from the hydrocarbon deposit. When conditions in the formation environment are favorable to rapid growth of the dispersed upstream metabolizers and methanogens, the relative populations of species in the consortium may become more weighted to these consortium populations. Thus, diluting an original consortium (e.g., a native consortium) with water may change the demographics of the microorganism members to increase the production of biogenic gases such as methane and hydrogen.

FIGS. 5A-B show flowcharts that illustrate methods of using water to stimulate biogenic gas production by a consortium of microorganisms. The method steps illustrated in FIG. 5A include forming an opening in a geologic formation 502 so water can be supplied to the microorganism consortium. The opening may be formed under conditions that limit the amount of atmospheric oxygen that flows into the opening. Formation of the opening may include boring, drilling, digging, blasting, excavating, etc., the opening starting at the surface of the formation. Embodiments also include unplugging or otherwise accessing a opening that has already been formed in the formation (e.g., a previously drilled oil well).

Following the formation of the opening, water may be injected into the opening 504. The water may have been extracted from the same formation, or have come from a different source, for example a different formation. The injected water may include live microorganisms, or the water may be treated to remove or inactivate the microorganisms. Removal treatments may include passing the water through a filter that collects the microorganisms in the retentate. Inactivation treatments may include heating and/or irradiating the water to kill the microorganisms present. Inactivation treatments may also include adding a biocide to the water to kill the microorganisms.

The water injected into the opening may disperse the consortium of microorganisms over a larger region of the formation 506. For example, if the consortium is concentrated in a specific region of a hydrocarbon deposit (e.g., a coal or oil deposit), the water may disperse the consortium over a larger region of the same deposit. The water may also dilute the consortium in a larger volume of fluid.

The rate of gas production may be measured 508 to determine the effect of injecting the water. Measured gases may include hydrogen, methane, carbon monoxide, and/or carbon dioxide, among other gases. The type of measurement may include a pressure measurement of the gases in the formation. This may involve partial pressure measurements of a particular gas (or group of gases), like the combustible gases methane and/or hydrogen. Measurements may be done before the water injection to establish a baseline rate of off-gassing in the formation. Additional measurements may be taken after the water injection to observe if the rate of gas production has changed as a result of the injection.

The water injection may be as simple as injecting a single sample into the opening. Embodiments may also include more complex patterns of water injection, where multiple cycles of water injection and extraction of fluids from the formation are performed. FIG. 5B shows a water injection pattern that includes the injection of two portions of water between an extraction step. Similar to FIG. 5A, the method may include forming an opening in a geologic formation 510 and injecting a first portion of water into the opening 512. A vacuum or some other type pressure differential may be applied to the opening to extract formation fluids from the opening 514. Following the extraction, a second portion of water may be injected into the opening 516. Measurement of the gas production rates 518 may be taken before, during and after the water injection cycle to determine how the injected water is affecting gas production rates in the formation.

It should be appreciated that the injection-extraction-injection cycle shown in FIG. 5B may include more iterations. It should also be appreciated that the volume of the water injected and the timing of the injection may be varied. For example, a first injection pattern may involve several injection cycles of smaller volumes of water, while a second pattern may involve fewer injection cycles of larger volumes of water.

Water injections and water treatments may also be done to change the salinity level of water in geologic formation. FIG. 6A shows steps in methods of controlling the salinity level of the water in a geologic formation according to embodiments of the invention. The methods may include measuring the salinity level in the formation water 602. If the salinity of the water is about 6% salt, by volume, or more (e.g., brackish or saline water) then some microorganisms in the formation environment may have reduced activity due to the high salt concentration. When the measured salinity level is high enough to interfere with the desired microorganism activity, an opening may be formed in the formation 604 that provides access for a water dilution amendment. Water having a reduced salinity level may be injected into the formation 608 through the opening. During the water injection, the salinity level of the in situ formation water may be monitored to quantify the impact of the water dilution. The salinity level in the formation water may continue to be monitored after the water injection to see if the salinity level starts to rise again. Measurements of metabolite production rates, such as production rates for hydrogen, methane, carbon monoxide, acetate, etc., may also be conducted 608 to gauge the impact of the reduced salinity level on biogenic activity.

The desired salinity level in a geologic formation depends in part on the microorganism consortium. Some native or introduced consortia are more active metabolizing carbonaceous substrates to metabolites with increased hydrogen content when the salinity level is about 6% or less. Some microorganism see further increases in activity when salinity levels reach about 3% or less. Some reach their highest activity levels at even lower salinity levels, such as a level approaching what is considered fresh water (i.e., less than about 0.05% salt, by volume). Embodiments of the invention include increasing, as well as decreasing, the salinity level of water in the formation to reach a desired salinity level. For example, if the salinity level of the water is too low, salt amendments may be introduced (e.g., sodium chloride, potassium chloride, etc.) to increase the salinity.

The water injected into the geological formation to change the salinity level of the water into the formation may come from an external source, or the formation itself. FIG. 6B is a flowchart illustrating steps in methods of changing the salinity by extracting, treating, and reintroducing water into same formation. The methods may include accessing the formation water in the geologic formation 652, and extracting a portion of the formation water 654. The salinity level of a sample of the extracted formation water is measured 656 to see if the water contains too much salt for significant metabolic production of carbon compound with enhanced hydrogen content.

If the salinity levels in the native formation water are too high, the extracted water may be treated to reduce the salinity level 658. A reduction in the salinity level of the water may be carried out by a variety of desalinization methods, including evaporation-condensation processes, multi-stage flash processes, electrodialysis reversal processes, reverse osmosis processes, freezing processes, and nanofiltration processes, among other processes. The desalinization process may reduce the salt concentration in the formation water to the level of fresh water (e.g, 0.05% or less salt, by volume), or end at higher salinity levels (e.g., about 2% salt, by vol., or less).

The reduced salinity formation water may then be reintroduced back into the geologic formation 658. Changes in the in situ salinity levels in the formation may be monitored during and after the reintroduction of the treated water. Concentrations and/or production rates for metabolite species in the formation (e.g., hydrogen, methane) may also be measured.

Embodiments of the invention also include extracting, desalinating, and reintroducing formation water to a geologic formation in an uninterrupted cycle. Thus, a first portion of native formation water may be extracted from the formation as a second portion is undergoing a desalinization process, and a third portion of treated water is being reintroduced to the formation, all at the same time. As additional cycles are completed, the salinity level of the formation water should be further reduced.

Definition of Salinity

Salinity is a measure of the dissolved salt concentration in water. The salts may include the dissolved ions of any ionic compounds present in the water. Common salts may include halide salts such as alkali metal halides (e.g., sodium chloride, potassium chloride, etc.) and alkali earth metal halides (e.g., magnesium chloride, calcium chloride, etc.). Salts may also include the salts of polyatomic cations and anions, such as ammonium salts, phosphate salts, nitrate salts, sulfate salts, and oxyhalide salts, among other kinds of salts.

The salinity level of “fresh water” is defined to have less than 0.05%, by vol, of salt. “Brackish water” has about 3% to 5% salt, by volume. “Brine” is defined as a concentrated salt solution that may be fully saturated at room temperature with one of more dissolved salt compound.

Experimental

Laboratory experiments were done to measure how changes in the levels of formation water can effect methane production from coal extracted under anaerobic conditions from a subterranean coal seam. Formation water was also recovered from the formation under anaerobic conditions (i.e., the formation water samples were not exposed to ambient air).

Three coal samples of coal were taken from the Dietz Coal seam (North West quadrant of the Powder River Basin). All three samples were separately placed in 125 ml serum bottles that were sealed in an anaerobic environment of argon gas. No formation water was added to the first sample bottle, while 0.2 ml of formation water was injected into the second sample bottle, and 2.0 ml of formation water is injected into the third sample bottle. The percentage of methane measured in the headspace above the coal in the bottles was then measured over a 1 year period. FIG. 7 shows the plot of the percentage of methane in the headspace of the bottles over time for the three samples.

FIG. 7 clearly demonstrates that the addition of formation water stimulates the production of methane from the coal samples. Additional radiocarbon labeling studies provided strong evidence that the methane was being biogenically produced. Thus, this experiment shows that formation water can stimulate the biogenic production of methane from carbonaceous substrates like coal.

The Experiment shows that the addition of the formation water increased the percentage of methane nearly three-fold in about 150 days. The present invention contemplates systems and methods for amending and transporting formation water to carbonaceous materials in formations on commercial scales. A proportional scaling of the resulting increase in methane production will make these formations, which include dormant oil and coal fields, commercially viable sources of methane, hydrogen, and other metabolites from the microbial digestion of carbonaceous substrates.

Additional experiments are proposed to measure the effects of consortium dilution and metabolite amendments on the production of biogenic gases. These include a first set of experiments for injecting water into a geologic formation containing coal. The coal deposit is an “active” coal that has been shown to produce methane from either biogenic processes (e.g., methanogenic microorganisms) or non-biogenic processes (e.g., methane desorption off the substrate, thermal breakdown of substrate, etc.). The water may be fresh water or salt water that has been filtered of microorganisms. This set of experiments compares changes in the rate of methane and hydrogen off-gassing based on how the water is introduced to the coal. For example, in one experiment, larger volumes of water are injected at higher pressure in fewer cycles, while a second experiment injects smaller volumes at lower pressure in more cycles. In these “huff and puff” experiments, fluids building up in the formation may also be extracted from between injection events. The measurements of the changes in the rates at which methane, hydrogen and other gases are building up in the formation offer insight into how a consortium of native microorganisms responds to the different patterns for water injection and extraction cycles.

A second set of experiments compares changes in the rate of methane and hydrogen off-gassing after introducing water to both active and inactive coals. The active coals demonstrated significant methane off-gassing prior to introducing the water, while the inactive coals showed very little pre-water off-gassing. The water used in these experiments is extracted from the formation itself and the native microorganism are not filtered or killed. In some experiments, the formation water may be extracted from the part of the formation in contact with the coal, while in others the water is taken from a different part of the formation. Different patterns of water injection cycles may also be compared for both the active and coal coals in this set of experiments.

A third set of experiments measures the effect of specific nutrient amendments on the rate of off-gassing from a deposit of active coal in a geologic formation. The nutrient amendments are added to water that's injected into the formation and onto the coal. The amendments may include a high concentration of yeast extract, a low concentration of yeast extract and phosphorous in various combinations. The water used comes for the formation. The same injection pattern is used for introducing the amended water to the coal to better attribute and correlate differences in off-gassing rates to the type of amendment used.

A fourth set of experiments introduces microorganism concentrates to an inactive coal deposit and measures changes in the off-gassing of gases such as hydrogen and methane. The microorganism concentrate may come from the retentate of filtered formation water. The experiments may use different injection patterns to introduce the microorganisms to the coal. The experiments may also dilute the concentrate to various levels (e.g., diluting the concentrate to 50%, 25%, 10%, etc., of its original concentration) to measure the effects of this dilution on the concentrate's ability to stimulate biogenic gas production.

A fifth set of experiments introduces hydrogen gas to the coals and measures its effect on the rate of off-gassing of methane. The experiments include introducing the hydrogen gas to both active and inactive coals. The hydrogen gas may be introduced after water has been introduced to the coals. In some of the experiments, microorganisms may also be introduced to the coal before its exposed to the hydrogen gas, or simultaneously therewith. Nutrient amendments, such as vitamins, minerals, yeast extract, phosphorous, phosphate, etc., may also be added.

A sixth set of experiments introduces acetate to the coals and measures its effect on the rate of off-gassing from the coal. The acetate may be introduced as an aqueous solution of acetic acid that's injected into the formation and onto the coal. Similar to the hydrogen gas experiments, the acetate experiments may be conducted on both active and inactive coals. Some of the experiments may include introducing microorganisms to the coal as well.

Tables 1A and B lists some of the experimental parameters for the six sets of experiments described above. It should be appreciated that the list in Tables 1A and B are not exhaustive, and different combinations of parameters (as well and additional parameters) may also be tried.

TABLE 1A Experimental Parameters for Six Sets of Experiments Cell Experimental Treatment Cells In Cells Grown Nutrient Water Cells Filtered Concentrate Set Summary Treatment on Surface Addition Source Out Added First Fresh Water Formation No None Any Water Yes No First Fresh Water Formation No None Any Water Yes No Second Water Flush Formation No None Same Well None No Second Water Flush Formation No None Same Well None No Second Water Flush Formation No None Same None No Formation Second Water Flush Formation No None Same None No Formation Third Nutritional Formation & No High YE Same None No Water Formation Third Nutritional Formation & No Low YE Same None No Water Formation Third Nutritional Formation & No P Same None No Water Formation Third Nutritional Formation & No High YE + P Same None No Water Formation Third Nutritional Formation & No Low YE + P Same None No Water Formation Fourth Inoculation Cell Conc. No Low MMV Specific to Yes Yes Cells Fourth Inoculation Cell Conc. No Low MMV Specific to Yes Yes Cells Fourth Grow and Cell Conc. No Low MMV Any Water Yes Yes - Diluted Dliute Fifth H₂ Add Formation No Low MMV Same Well Yes No Formation Fifth H₂ Add Formation & No Low MMV Same Well No No Both Water Fifth H₂ Add Water Yes Low MMV Same No No Water Formation Fifth H₂ Add Water Yes Low MMV Any Water Yes Yes New Cells Sixth Acetate Add Formation No Low MMV Same Well Yes No Sixth Acetate Add Formation & No Low MMV Same Well No No Water Sixth Acetate Add Water Yes Low MMV Same No No Formation Sixth Acetate Add Water Yes Low MMV Any Water Yes Yes

TABLE 1-B Experimental Parameters for Six Sets of Experiments (con't) Number of Big or Small Experimental Injection Injection High or Low Water Level Water Wash Number of Set Cycles Volume Pressure Over Coal Active Coal First? Wells First Several Small Low No Yes N/A Few First Few Big High No Yes N/A Several Second Several Small Low No Yes No Several Second Few Big High No No No Several Second Several Small Low No Yes No Few Second Few Big High No No No Several Third Few Big High No Yes No Several Third Few Big High No Yes No Several Third Few Big High No Yes No Several Third Few Big High No Yes No Several Third Few Big High No Yes No Several Fourth Several Small Low No No Maybe Few Fourth Few Big High No No Maybe Several Fourth Several Small Low No No Yes Few Fifth Several Small Low Yes Yes Maybe Few Fifth Several Small Low Yes No Maybe Few Fifth Several Small Low No No Yes Few Fifth Several Small Low No No Yes Few Sixth Several Small Low No Yes Maybe Few Sixth Several Small Low No No Maybe Few Sixth Several Small Low No No Yes Few Sixth Several Small Low No No Yes Few

In Tables 1A-B the nutrient addition “MMV” indicates metals, minerals and/or vitamin amendment was made; “YE” indicates a yeast extract amendment was made; and “P” indicates phosphate amendment was made.

Examples of mineral amendments may include the addition of chloride, ammonium, phosphate, sodium, magnesium, potassium, and/or calcium to the isolate, among other kinds of minerals. Metal amendments may include the addition of manganese, iron, cobalt, zinc, copper, nickel, selenate, tungstenate, and/or molybdate to the isolate, among other kinds of metals. Vitamin amendments may include the addition of pyridoxine, thiamine, riboflavin, calcium pantothenate, thioctic acid, p-aminobenzoic acid, nicotinic acid, vitamin B12, 2-mercaptoehanesulfonic acid, biotin, and/or folic acid, among other vitamins. The addition of these amendments may involve adding mineral salts, metal salts, and vitamins directly to the isolate, or first preparing a solution of the salts and vitamins that then gets added to the isolate.

The concentration of the MMV, YE and P amendments may depend on the concentration and composition of an isolated consortium. Examples of concentration ranges for amendment components may include about 1 mg/L to about 500 mg/L for mineral amendment; about 10 μg/L to about 2000 μg/L for a metal amendment; and about 1 μg/L to about 100 μg/L for a vitamin amendment.

Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the electrode” includes reference to one or more electrodes and equivalents thereof known to those skilled in the art, and so forth.

Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups. 

1. A method to stimulate the biogenic production of a combustible gas from a hydrocarbon substrate in a subterranean geologic formation, the method comprising: forming an opening in a geologic formation to provide access to a consortium of microorganisms; measuring a salinity level in formation water extracted from the geologic formation; injecting water into the opening, wherein the injected water changes the salinity level of the formation environment for at least a portion of the microorganism consortium; and recovering the combustible gas from the formation environment.
 2. The method of claim 1, wherein the combustible gas comprises hydrogen or methane.
 3. The method of claim 1, wherein the hydrocarbon substrate includes one or more materials selected from the group consisting of coal, oil, kerogen, peat, lignite, oil shale, tar sands, bitumen, and tar.
 4. The method of claim 1, wherein the injected water decreases the salinity level of the formation environment for at least a portion of the microorganism consortium.
 5. The method of claim 4, wherein the injected water is formed from the formation water extracted from the geologic formation that has been treated to reduce its salinity level.
 6. The method of claim 4, wherein the salinity level in the formation water is greater than 0.05 vol % salt and the injected water comprises less than about 0.05 vol. % salt.
 7. The method of claim 4, wherein the salinity level in the formation water is about 3 vol. % salt or more.
 8. The method of claim 4, wherein the salinity level in the formation water is about 6 vol. % salt or more.
 9. The method of claim 1, wherein the method further comprises measuring a change in a production rate of the combustible gas recovered from the formation environment.
 10. A method to adjust a salinity level of formation water from a geologic formation to stimulate the biogenic production of a combustible gas from a hydrocarbon substrate in the formation, the method comprising: extracting a portion of the formation water from the geologic formation; measuring the salinity level of the formation water; adjusting the salinity level of the formation water to a target salinity level; and introducing at least a portion of the extracted formation water to the geologic formation; and recovering the combustible gas from the formation environment. 